Improved Limits on Spin-Mass Interactions

Junyi Lee, Attaallah Almasi, Michael Romalis

Research output: Contribution to journalArticlepeer-review

97 Scopus citations


Very light particles with CP-violating couplings to ordinary matter, such as axions or axionlike particles, can mediate long-range forces between polarized and unpolarized fermions. We describe a new experimental search for such forces between unpolarized nucleons in two 250 kg Pb weights and polarized neutrons and electrons in a He3-K comagnetometer located about 15 cm away. We place improved constraints on the products of scalar and pseudoscalar coupling constants, gpngsN<4.2×10-30 and gpegsN<1.7×10-30 (95% C.L.) for axionlike particle masses less than 10-6 eV, which represents an order of magnitude improvement over the best previous neutron laboratory limit.

Original languageEnglish (US)
Article number161801
JournalPhysical review letters
Issue number16
StatePublished - Apr 17 2018

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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